Designs for measure-while-drilling (“MWD”) siren telemetry modulators are based on a rotating seal with drilling fluid (“mud”) on one side of the seal and another fluid, generally an oil, on the opposite side of the seal. Compensation for changes in oil temperature or pressure across the seal is done by a reactive spring system in conventional systems. The reactive spring system attempts to limit particulate contamination within the telemetry modulator by providing a sealing pressure between the rotating seal and the body of the modulator. The spring system is provided with a spring constant, “K”, that provides a specified reaction force. The greater the deflection of the spring system from its intended bearing point, the greater the force the spring system exerts to bring the spring system back into a desired position.
Such conventional designs and systems for sealing modulators are not without problems. Problems associated with these systems include failure of the sealing system, allowing contaminants to affect system operation. Such conventional systems are expensive to produce, not withstanding their physical limitations. Production of high quality springs can be troublesome and springs can break or fatigue under many repeated cycles. Repeated forces/loadings, over time, can cause the reactive spring system to eventually fail. Such systems have a further drawback of not being able to react quickly enough to changes in temperature or pressure of the fluid. Late reaction in changes to temperature and pressure causes repeated cycles of stress that can lead to over-pressurization or failure of components within the system. Moreover, reactive spring systems are purely reactive and can not anticipate loadings. These reactive spring systems deflect once the loading is placed upon the system. These systems have no potential anticipatory loading capability.
There are many systems that can be used to reduce vibrations or to improve vibration resistance. Such systems include shock absorbers for automobiles that allow control of unequal damping over time. In an example embodiment, provided in U.S. Pat. No. 5,883,447, two active masses are provided that are driving in a planar motion, an arrangement of two flexible cylindrical plates and a plurality of motors. Systems may also be used that provide configurations of electrically active/magnetically active fluids that provide progressive resistance over time, rather than use a mechanical spring action force mechanism. Such systems, however, must be very carefully controlled and are not applicable for use in high temperature environments or other harsh conditions.
In an alternative system, described in U.S. Pat. No. 7,083,008, a reactive compensation system is provided for a borehole device that attempts to provide compensation but still has significant drawbacks.
There is a need to provide a system that can withstand repeated forces and loadings over time that is easy and cost effective to produce.